1. Field of the Invention
The present invention relates to a method for fabricating a semiconductor device and a semiconductor device, for example, a semiconductor device in which a contact plug to connect a device portion to a wire such as a copper (Cu) wire is arranged and a method for fabricating a semiconductor device.
2. Related Art
In recent years, a new micropatterning technique is developed with advancing of the integration density and performance of a semiconductor integrated circuit (LSI). In particular, recently, in order to achieve the advancing of the high-speed performance of an LSI, an action that replaces a wire material from a conventional aluminum (Al) alloy into low-resistance copper (Cu) or a Cu alloy (to be collectively referred to as Cu hereinafter) is gaining. With recent micropatterning of the semiconductor integrated circuit described above, a contact hole to connect a Cu wire to a substrate diffusion layer and a contact hole to connect a Cu wire to a source, a drain and a gate electrode of a transistor decrease in diameter. Accordingly, aspect ratios of the contact holes increase. For this reason, an increase in contact resistance in a contact plug becomes serious.
For example, a conventional contact plug is formed as follows. Titanium (Ti) is deposited on a substrate surface, a contact hole wall surface, and a contact hole bottom surface. Titanium silicide (TiSi2) is formed on a silicon (Si) substrate on the bottom surface. On the other hand, Ti on the contact hole wall surface is nitrided to form titanium nitride (TiN). Thereafter, the contact hole is buried with a tungsten (W) film to form a contact plug (for example, see Published Japanese Translation No. 2001-523043 of the PCT International Publication).
In this case, when the W film serving as a plug is formed, a chemical vapor deposition (CVD) method which supplies a tungsten hexafluoride (WF6) gas, hydrogen (H2) serving as a reducing gas, and the like is used. At this time, if a barrier metal layer is not formed, fluorine (F) of WF6 performs F-attack the contact hole bottom surface during film formation of the W film to damage a contact interface and to influence the characteristics of the device. For this reason, as described above, the barrier metal layer is formed in advance to prevent the F attack. Furthermore, from this viewpoint, by a thermal CVD method using an organic Ti material, a thermal CVD method using titanium tetrachloride (TiCl4) serving as an inorganic material, and the like, formation of a TiN film on a Ti film or further growth of a TiN film after the Ti film is nitrided are also attempted.
On the other hand, with advancing of the integration density of a recent semiconductor integrated circuit, a contact hole decreases in diameter. Although the contact hole decreases in diameter, when a TiN film serving as a barrier metal is formed to have the same thickness as that used when a contact hole has a large diameter, a volume of a W film for a contact plug reduces. For this reason, a ratio of the volume of the high-resistance TiN film to the volume of the W film increases, and a contact resistance disadvantageously increases accordingly.